Nitrogen metabolism in haloarchaea

The nitrogen cycle (N-cycle), principally supported by prokaryotes, involves different redox reactions mainly focused on assimilatory purposes or respiratory processes for energy conservation. As the N-cycle has important environmental implications, this biogeochemical cycle has become a major research topic during the last few years. However, although N-cycle metabolic pathways have been studied extensively in Bacteria or Eukarya, relatively little is known in the Archaea. Halophilic Archaea are the predominant microorganisms in hot and hypersaline environments such as salted lakes, hot springs or salted ponds. Consequently, the denitrifying haloarchaea that sustain the nitrogen cycle under these conditions have emerged as an important target for research aimed at understanding microbial life in these extreme environments. The haloarchaeon Haloferax mediterranei was isolated 20 years ago from Santa Pola salted ponds (Alicante, Spain). It was described as a denitrifier and it is also able to grow using NO3-, NO2- or NH4+ as inorganic nitrogen sources. This review summarizes the advances that have been made in understanding the N-cycle in halophilic archaea using Hfx mediterranei as a haloarchaeal model. The results obtained show that this microorganism could be very attractive for bioremediation applications in those areas where high salt, nitrate and nitrite concentrations are found in ground waters and soils.

Fortification and Frontier: The Project Drawn up by Juan Martín Zermeño for Puebla de Sanabria in 1766

Following the death of engineer General Jorge Próspero de Verboom in 1744 and after a few years of transition in the management of Spanish fortifications, Juan Martín Zermeño took on the role, initially with a temporary mandate, but then definitively during a second period that ran from 1766 until his death in 1772. He began this second period with a certain amount of concern because of what had taken place during the last period of conflict. The Seven Years War (1756–1763) which had brought Spain into conflict with Portugal and England in the Caribbean had also lead to conflict episodes along the Spanish–Portuguese border. Zermeño’s efforts as a planner and general engineer gave priority to the northern part of the Spanish–Portuguese border. After studying the territory and the existing fortifications on both sides of the border, Zermeño drew up three important projects in 1766. The outposts that needed to be reinforced were located, from north to south, at Puebla de Sanabria, Zamora and Ciudad Rodrigo, which is where he is believed to have come from. This latter township already had a modern installation built immediately after the war of the Spanish Succession and reinforced with the Fort of La Concepción. However, Zamora and Puebla de Sanabria had some obsolete fortifications that needed modernising. Since the middle of the 15th century Puebla de Sanabria had had a modern castle with rounded turrets, that of the counts of benavente. During the 16th and 17th centuries it had also been equipped with a walled enclosure with small bastions. During the war of the Spanish Succession the Portuguese had enlarged the enclosure and had erected a tentative offshoot to the west. In order to draw up the ambitious Puebla de Sanabria project Zermeño had the aid of some previous reports and projects, such as those by the count of robelin in 1722, the one by Antonio de Gaver in 1752, and Pedro Moreau’s report dated June 1755. This study includes a technical analysis of Zermeño’s project and its strategic position within the system of fortifications along the Spanish–Portuguese border.